Field of the Invention
This invention relates to temperature sensing devices and more particularly to temperature sensing devices that can be implanted within the body of humans or other animals.
Research has disclosed that tissue and tumors in animals may be destroyed by a selective increase in temperature. Relatively small elevations of temperature are adequate to effect destruction. When this technique is used to destroy tumors, great care must be taken to avoid injury to the surrounding tissue. Accordingly, it is important to precisely monitor the temperature of the tumor and the surrounding tissue.
While the desired heating may be accomplished in a variety of ways, the present application is principally concerned with operations wherein an electromagnetic field is used. In the presence of such a field, many temperature sensing devices either become inoperative or perturb the field and adversely affect the procedure. Any conductive material, line or element, placed within an electromagnetic field will have a radio frequency current induced within it. Such a current in turn causes a new electromagnetic field to be established and such a new field alters the original incident field. It has been found that by utilizing extremely high resistances in the temperature monitoring unit, negligible current will flow and there will therefore be no perceptible perturbation of the incident field. Furthermore, by utilizing high resistance within the monitoring unit, the negligible currents that are induced will provide extremely low power dissipation and hence there is negligible localized heating originated by the unit itself.
Description of the Prior Art
A variety of temperature probes have been recently proposed. One such unit employs a liquid crystal located at the end of a fiber optics bundle and measures temperatures within a limited range. Since this probe has no metallic components it has little effect upon electromagnetic radiation. Another unit uses a thermistor and plastic high-resistance leads. The thermistor resistance is sensed by injecting a constant current through a first pair of leads while measuring the voltage developed across the thermistor with a high impedance amplifier connected to a second pair of leads. Still another unit consists of a microwave integrated circuit electrode having a transducer that is glass encapsulated and a hyper-thin transmission line for r-f decoupling.